Comment by mnw21cam

A tenth is perhaps an exaggeration. It depends on how you count your lifespan.

A lead-acid battery mainly ages by cycle count. If you keep a decent quality battery charged up, and don't regularly discharge it too much, then there are claims they will last ten years. If you discharge them excessively each day, then you'll kill them really quickly.

A LiFePO4 battery has a quoted cycle count. But really what matters is simply elapsed time - the battery will last about ten years if it isn't abused, and you'll be hard-pressed to actually do that many cycles in that ten years. It ages mainly by elapsed time, not cycle count.

I used to argue that for an off-grid solar solution, you should get lead-acid batteries with capacity so that you are normally never discharging below 70%, and that this was still cheaper than getting LiFePO4 batteries with smaller capacity that you would discharge down to 20% each night. The lead-acid would then give you a larger reserve capacity for those instances where the weather is foul for a bit longer than normal and you don't get meaningful charging.

However, since then LiFePO4 batteries have continued to decrease in price, there are new Sodium batteries available now, and I haven't done the calculations again - the best option may have switched over, or it may be so close that it doesn't really matter which one you choose.